The present invention relates to cooling apparatus for controlling the operating temperature of lubricants, and in particular, it is directed to controlling the operating temperature of a gear lubricant contained in an automotive differential by providing a differential cover plate having an air duct arrangement includes means to selectively force a stream of cooling air across the surface of the differential cover plate to remove heat therefrom and thereby reduce the operating temperature of the gear lubricant contained within the differential housing.
It is well known that under certain load conditions the operating temperature of automotive lubricants and motor oils can be raised to temperature levels where they lose their viscosity. Hot, thinned gear lubricants and motor oils fail to provide adequate lubrication when they loose their viscosity. This can cause premature wear and/or damage to gears and engine parts, and it reduces the service life of components in both the engine and power train of the vehicle. This is especially true in a 4-wheel drive vehicle that is driven at either very fast highway speeds, or on extremely rough off-road conditions. Such high speed travel and/or heavy off-road conditions produce high operating temperatures in the differentials of 4-wheel drive vehicles, and the high gear lubricant temperature results in premature gear wear and failure.
The above described problem of high lubricant temperatures is not limited to 4-wheel drive vehicles. For example, high temperature problems are also experienced in recreational vehicles, including motor homes of all sizes, as well as any vehicle that tows a load ranging from a small boat to utility trailers and campers of all sizes and weights. The large size and mass of recreational vehicles, and the additional weight of a tow, impose loads on drive train components that produce high lubricant temperatures.
High operating temperatures are also a problem for high performance vehicles such as race cars. These vehicles are driven at sustained high speeds over long periods of time, and they often breakdown during a race due to mechanical failures caused by very high racing temperatures that cause lubricant failure.
Various attempts to overcome such high temperature problems are well documented in earlier patents. For example. United States patents granted to Downs, et al., Baedke, et al. and Hayashida, et al., teach various means for lowering the operating temperature of gear lubricant contained within an automotive differential. The Hayashida patent teaches using an air cooled heat exchanger to lower the operating temperature of a differential lubricant. The inventors disclose an automotive differential that includes a remote oil cooler and an air duct for directing air across the oil cooler. The cooling airflow is generated by, and dependent upon the speed of forward motion of the vehicle. The flow of air across the oil cooler lowers the temperature of the gear lubricant in the cooler, and the cooled lubricant is recycled back into the differential. The Downs and Baedke patents also teach remote cooling apparatus that is dependent upon the forward speed of vehicle travel to generate a flow of cooling air that lowers the operating temperature of lubricant.
The apparatus taught in these prior patents are limited in providing lubricant cooling because they are dependent upon the forward rate of vehicle travel, and they fail to provide sufficient cooling at slow vehicle speeds. They also completely fail to provide lubricant cooling when the vehicle is at a standstill.
Under heavy off-road conditions, where the terrain is extremely rough, operators of 4-wheel drive vehicles often drive at very slow rates of speed in order to navigate the various rough steep and rocky obstacles that they encounter. Such torturous operating conditions elevate the differential gear lubricants to very high temperatures above about 250.degree. F. The prior patents teach apparatus that requires fast forward travel by the vehicle to generate an airflow for cooling a lubricant. The patents fail to recognize any problems associated with slow, off-road vehicle travel, and their teaching fails to even suggest a means to overcome such problems.
Various other patents disclose using fans or blowers to generate a flow of air to cool non-automotive mechanisms. For example, Jorg discloses an arrangement for cooling a gear case by means of a fan connected to the gear mechanism being cooled. The fan is attached directly to the power train of the transmission device and operates continuously while the gear mechanism is running. The patent completely fails to teach or even suggest providing means to selectively engage or disengage the fan in response to a need to cool. Such devices are unsuitable for automotive applications, and in particular, they are unsuitable for automotive use under frigid conditions. At sub-zero temperatures it is desirable to run vehicles at idle to warm up lubricants prior to actual vehicle operation. Under extreme frigid conditions, auxiliary heating is often supplied to vehicle parts to bring lubricants up to operating temperature. This practice avoids damaging tight fitting engine and transmission parts that would fail to have adequate lubrication with thick cold lubricants. An example of such auxiliary heating means is shown in the Brown patent that teaches attaching a heater to a differential housing in order to bring the gear lubricants up to operating temperature prior to vehicle start up.